poj2104 K大数 划分树

题意:给定一个数列,求一个区间的第K大数

模板题, 其中的newl, newr 有点不明白.

 #include <iostream>
 #include <algorithm>
 using namespace std;
 const int M = ;
 int toLeft[][M], tree[][M], sorted[M];

 void build(int level, int left, int right)
 {
     if (left == right) return;
     int i, mid = (left + right) >>;
     int suppose = mid - left + ;
     for (i=left; i<=right; i++)
         if (tree[level][i] < sorted[mid])
             suppose--;
     int lpos = left, rpos = mid+;
     for (i=left; i<=right; i++)
     {
         if (i == left)
             toLeft[level][i] = ;
         else
             toLeft[level][i] = toLeft[level][i-];
         if (tree[level][i] < sorted[mid])
         {
             toLeft[level][i]++;
             tree[level+][lpos++] = tree[level][i];
         }
         else if (tree[level][i] > sorted[mid])
         {
             tree[level+][rpos++] = tree[level][i];
         }
         else
         {
             if (suppose != )
             {
                 suppose--;
                 toLeft[level][i]++;
                 tree[level+][lpos++] = tree[level][i];
             }
             else
                 tree[level+][rpos++] = tree[level][i];
         }
     }
     build(level+, left, mid);
     build(level+, mid+, right);
 }

 int query(int level, int left, int right, int qleft, int qright, int k)
 {
     if (qleft == qright)
         return tree[level][qright];
     int s, ss, mid = (left + right)>>;
     if (left == qleft)
     {
         s = ;
         ss = toLeft[level][qright];
     }
     else
     {
         s = toLeft[level][qleft-];
         ss = toLeft[level][qright] - s;
     }
     int newl, newr;
     if (k <= ss)
     {
         newl = left + s;
         newr = left + s + ss -;
         return query(level+, left, mid, newl, newr, k);
     }
     else
     {
         newl = mid-left++qleft-s;
         newr = mid-left++qright-s-ss;
         return query(level+, mid+, right, newl, newr, k-ss);
     }
 }

 int main()
 {
     int n, m;
     int i;
     while (scanf("%d%d", &n, &m) == )
     {
         for (i=; i<=n; i++)
         {
             scanf("%d", &tree[][i]);
             sorted[i] = tree[][i];
         }
         sort(sorted+, sorted+n+);
         build(,,n);
         int ql, qr, k;
         for (i=; i<m; i++)
         {
             scanf("%d%d%d", &ql, &qr, &k);
             printf("%d\n", query(, , n, ql, qr, k));
         }
     }
     return ;
 }